Refractory bodies containing boron nitride and a boride, and the manufacture thereof



United States REFRACTORY BODIES CONTAINING BORON NI- TRIDE AND A BORIDE,AND THE MANUFAC- TURE THEREOF No Drawing. Application October 25, 1954Serial No. 464,655

13 Claims. (Cl. 105-55) This invention relates to shaped bodies orarticles of ,manufacture consisting essentially of refractory boride andboron nitride, and to compositions and methods for making the same. Thispatent application is a continuatlon-m-part of my co-pending applicationSerial No.

288,554, filed May 17, 1952, now abandoned.

There is a constant search for new compositions or bodies that possessunexpected combinations of properties essential to or desirable inspecific fields of use. The

. bodies of the present invention possess certain combinations ofproperties and characteristics that render them of considerable value,and they offer outstanding possibilities in a number of fields of use.It is, therefore, to be understood that the refractory boride-boronnitride bodies hereinafter more fully described are not to be consideredas restricted to any particular field of use. However, their outstandingcharacteristics as refractory materials are particularly worthy of noteand make them especially suitable for many refractory purposes. Thepresent invention therefore will be described primarily in respect tousing the herein described products for refractory purposes, althoughnot intended to be limited thereto.

Above all a refractory body must possess refractoriness, that is,ability to stand up under exposure to high temperatures without unduechemical or physical change. Other desirable characteristics sought in arefractory body or shape include an ability to resist sudden changes intemperature without cracking or otherwise breaking down, asatisfactorily high mechanical strength at elevated temperatures as wellas at room temperature, chemical inertness and resistance to variouscorrosive and erosive substances and conditions, a resistance tooxidation, anda density and hardness dependent upon the use to which therefractory body or shape is to be put.

In order to obtain a high degree of perfection in one or more of theabove properties, it has usually been necessary to forego the benefit ofmaximum performance in respect to certain other desirable properties.Consequently, various refractory compositions exceptionally suited forone use frequently are entirely unsatisfactory for other purposes. Thereis, therefore, a continual need for refractory bodies of new compositionthat will meet those demands of a special nature which require novelcombinations of properties not to be found in compositions alreadyavailable.

It is an object of the present invention to provide bonded refractorybodies or shapes of unusual and distinctive compositions and properties.

It is another object to provide refractory bodies or shapes having aparticular combination of properties heretofore unavailable inrefractory compositions.

It is another object to provide novel compositions of matter consistingessentially of refractory boride material and boron nitride.

It is a further object to provide practical methods and compositions formaking such articles.

The shapes or bodies of the present invention comprise 2,872,327Patented Feb. 3, 1959 boron nitride and refractory boride material. Theamount of boron nitride present in the bodies may range from almost 0%,such as 1 or 2%, to almost by weight of the bodies. The preferredcompositions of the present invention, however, contain only up to about50% by Weight boron nitride, with the best bodies containing not overabout 20% by weight boron nitride.

The bodies or articles of the present invention are made by hot-pressingthe raw mixes in a graphite mold ata temperature somewhat lower than thetemperature at which the particular raw mix becomes so plastic as to beextruded from the mold around the plunger. With compositions high inboride content, the maximum hot-pressing temperature is usually slightlybelow the melting temperature of the boride. The hot-pressing ispreferably carried on at pressures of from 500 to 750 pounds per squareinch or more.

The boron nitride used in carrying out the present invention may beeither a high or low purity boron nitride material available on themarket. For example, it may be an impure boron nitride made inaccordance With the process described in my copending United Statespatent application Serial No. 288,553, which issued October 1, 1957, asU. S. Patent No. 2,808,314. This boron nitride material is made bynitriding a porous pelleted mixture of boric acid or boric oxide andtricalcium phosphate by heating it in ammonia gas at a temperature ofaround 900 C. After nitriding the resulting nitrided pellets are treatedwith dilute hydrochloric acid to dissolve the tricalcium phosphate andother extraneous materials. The undissolved boron nitride, after Washingwith Water, is usually treated with hot 95% alcohol solution to furtherlower the content of extraneous materials. The material is then dried byallowing it to stand overnight at room temperature followed by heatingfor two hours at 300 F. A typical analysis of the boron nitride is asfollows:

Percent Boron 41.45 Nitrogen 44.00 Free boric acid (calculated as H BO.75 Silica .28 Calcium Trace Phosphate (P0 Trace Material volatile at C.26 Extraenous matter, estimated to be combined oxygen 13.26

Although this material contains no alcohol soluble material, it isbelieved that it contains up to about 20% of an oxidic boron compoundcombined either chemically or physically so as to be insoluble inalcohol and Water.

An example of a high purity boron nitride material that may be used inthe process of the present invention is the material made in accordancewith the process described in my United States patent application SerialNo. 413,968. Boron nitride material is made in accordance with thispatent application by first preparing a low purity boron nitridematerial, such as the boron nitride material prepared in accordance withthe process of my above-mentioned patent application Serial No. 288,553,and then heating the low purity boron nitride material in an atmosphereof ammonia at a temperature ranging from about 1100 to 1500 C. A typicalanalysis of the resulting high-purity boron nitride material is asfollows:

Percent 43.3

2.23 0.25 Nil 0.16

I have further found that if boron nitride prepared in accordance withmy patent application Serial No. 288,553, is subsequently, before use,subjected to a heating pre-treatment in which the material is heated inan inert atmosphere at a temperature in the neighborhood of 1900 to 2200C., molded shapes containing the thus treated material are superior forcertain uses.

The refractory boride material employed in the process of the presentinvention may be any of the wellknown refractory borides, preferablybeing selected from the group consisting of zirconium boride, titaniumboride, molybdenum boride, chromium boride, carbon boride, and mixturesthereof.

raised to approximately 2100 C. over a period of 1 /2 hours and held atapproximately 2100 C for 10 minutes under a minimum pressure of 500 p.s. i. The furnace was then allowed to cool to room temperature. Thefurnace chamber was cylindrical, 12 long and 4" inside diameter and wasclosed during the heating and cooling periods except for an opening inthe top about one half inch in diameter through which temperatureobservations were made, Table I below presents fabricating data andphysical properties of the various bodies consisting essentially ofboron nitride and zirconium boride made in accordance with this exampleof the process of the present invention.

Table I BODIES CONSISTING ESSENTIALLY OF BORON NITRIDE AND 1 Standardpenetration on plate glass when subjected to the same penetration testis .010"

The refractory borides used in carrying out the present invention may beany high purity grade of refractory boride available on the market.However when borides other than carbon boride are used in carrying outthe present invention, it is preferred to use a product made inaccordance with K. C. Nicholson United States patent application SerialNo. 252,190. Briefly the process for the manufacture of metal borides,such as ZrB and TiB in accordance with this patent application comprisesreacting a mixture of metal oxide, boron carbide and carbon and/ ormetal to produce metal boride.

EXAMPLE II Boron nitride-refractory boride bodies using other metalborides were made in accordance with the procedures set forth in ExampleI, except that the boron nitride was prepared as per patent applicationSerial No. 413,968 and certain of the bodies were hot-pressed attemperatures lower than the temperature employed in Example I. Table IIbelow presents fabricating data and physical properties of the variousbodies consisting essentially of boron nitride and refractory boride.

Table II BODIES CONSISTING ESSENTIALLY 0F BORON NITRIDE AND METAL BORIDERaw Mix composition, Molding Molding Sandblast Apparent Bar No.Percentage by Weight Pretreatment of BN Temp., Pressure, Pcnetra-Density, O. p. s. t. tion inches gms/ce.

5 20% EN; 80% ZrBz Prlegitil'ggn N; at 2, 000 2, 000 3. 49 15% EN; 85%Mo2B-...- Prgiggl N2 at 1,600 2,000 .005 5. 75

1.. 15% EN; 85% CHE"--- Prefirsgi 2.311 N: at 1, 600 2, 000 009 4. 1580% EN; 20% Tush--- Nohem": 1,800 2,000 .008 2. 24

1 Standard penetration on plate glass when subjected to the samepenetration test is .010".

EXAMPLE I Raw mixes consisting essentially of boron nitride (made as perpatent application Serial No. 288,553) and finely divided zirconiumboride were mixed by grinding together for 24 hours in alcohol in a ballmill lined with sintered tungsten carbide. The resulting mixtures wereplaced in a cylindrical graphite mold having two movable graphiteplungers. The assembled mold was placed in a graphite chamber of a highfrequency furnace and heated as follows: The temperature of the mold wasEXAMPLE III Twenty parts by weight of boron nitride and eighty parts byweight of carbon boride were thoroughly dry mixed. The boron nitride waspreviously prefired in ammonia gas at 1400 C. for eight hours. Thecarbon boride, otherwise known as boron carbide, was mesh and finermaterial obtained from The Norton Company, Worcester, Massachusetts.Nine grams of the resulting mixture were placed in a cylindricalgraphite mold having an inside diameter of approximately /2" and havingtwo movable graphite plungers. The assembled mold was placed in acylindrical graphite chamber 4" inside diameter and 12" length in a highfrequency furnace having means for applying pressure to the plungers ofthe mold. The chamber of the furnace was closed except for an opening inthe top about /2" in diameter through which temperature observationswere made. The temperature of the furnace was raised to 2100 C. over aperiod of about 1 /2 hours and maintained at approximately thattemperature for amout 10 minutes, and

we e? then allowedto coolto room temperature. A pressure of 750 poundsper square inch was maintained on the plung'ers of the mold during theheating and cooling periods.

The resulting hot pressed piece was dense, strong and hard, the apparentdensity being 2.25 gms./cc. The sandblast penetration was .003 ascompared to the penetration on plate glass by the same test of .010".

The resulting shape further showed a relatively satisfactory resistanceto oxidation, the article undergoing a weight loss of only 1.8% afterheating in air for 24 hours at 1000 C.

Table III presents fabricating data and properties of hot pressed bodiesof boron nitride and carbon boride. Table III below and other experiencealso show the greater hardness of bodies composed of boron nitride andcarbon boride when the percentage of boron nitride is lowered from 50%to around by weight of the body. The boron nitride was prefired at 1400C. prior to incorporation in the mixtures from which the bodies weremade.

Standard penetration on plate glass when subjected to the samepenetration testis .010 of an in Z Pretlred in ammonia 8 hours at 1.400"0.

While I have described in the above examples the making of variousmolded bodies in which the body is molded and fired to the exact shapeand form in which it is intended for use, the present invention is notintended to be so restricted. Another way of making and usingnitride-boride bodies of the present invention is to mold the raw batchof material into briquettes or other shapes or otherwise compress a massof the material having a composition in the desired proportions, afterwhich the resulting briquettes or compressed bodies are hot pressed in amanner already described. After removal from the furnace, they arecrushed to granular form of the desired grit size. The resultinggranular material can then be used in loose granular form as a hightemperature refractory material or as a layer of high temperatureinsulation material, as, for example, insulation or protection aroundjet engines and rocket combustion chambers, or as a layer of insulationaround industrial furnace chambers. It may also be used as a loosefiltering media or as a catalyst or catalyst carrier material. Thegranular material can also be bonded by means of sintered metals,vitreous or ceramic bonds or other bonding material to form articlessuitable for many' of the industrial uses set forth elsewhere herein.

It is to be understood that the products of the present invention in itsvarious modifications are not limited to any specific field or fields ofuse such as might be defined by the specific examples previously setforth. The products can be made in any desired shape as well as providedin granular or aggregate form. They are, therefore, not only suited formany of the uses for which industrial refractories are required,including bracks, blocks, setter tile, muffles, kiln furniture, andspecial shapes for application in and around furnaces and other hightemperature equipment, but they are also Well suited for many specialtyhigh temperature applications, such as jet engine combustion chambers,lining for exhaust noz- Zles, rocket combustion chambers and exhaustnozzles,

turbine blades,- stator blades, lens fusion blocks, and the like. Theyare also suitable for the fabrication of laboratory Ware, includingcombustion boats, crucibles, burner holders, and other shapes. Thebodies of the present invention, particularly when modified by the useof pore formers in the raw batch from which the bodies are made, arealso highly useful as diffusion and filtering media, such as diffusiontubes and plates, filtering tubes, plates and shapes, or as catalysts orcatalyst carriers and supports. Materials and articles of the presentinvention can also be used for making abrasive articles such as grindingwheels, sharpening stones, razor bones, and other grinding and polishingshapes and materials. The present bodies offer possible applications inthe electrical and radio industry including supports in electric lightbulbs, radio tubes, X-ray tubes and radar equipment, resistors and gridleaks.

Having described the present invention it is desired to claim:

1. As a new article of manufacture, a body consisting essentially ofboron nitride and boride selected from the group consisting of zirconiumboride, titanium boride, molybdenum boride, chromium boride, carbonboride, and mixtures thereof, the boride amounting to 20% to 99% byweight of the body.

2. As a new article of manufacture, a body consisting essentially ofboron nitride and boride selected from the group consisting of zirconiumboride, titanium boride, molybdenum boride, chromium boride, carbonboride and mixtures thereof, boron nitride amounting to 1% to by weightof the body.

3. As a new article of manufacture, a body consisting essentially ofboron nitride and boride selected from the group consisting of zirconiumboride, titanium boride, molybdenum boride, chromium boride, carbonboride and mixtures thereof, said boride amounting to 50% to 99% byweight of the body.

4. A refractory article consisting essentially of zirconium boride andboron nitride, boron nitride being present in said article from 1% to50% by weight.

5. A refractory article consisting essentially of titanium boride andboron nitride, boron nitride being present in said article from 1% to50% by weight. g

6. A refractory article consisting essentially of molybdenurn boride andboron nitride, boron nitride being present in said article from 1% to50% by weight.

7. A refractory article consisting essentially of chromium boride andboron nitride, boron nitride being present in said article from 1% to50% by weight.

8. A refractory article consisting essentially of carbon boride andboron nitride, boron nitride being present in said article from 1% to50% by weight.

9. A method of making bonded shapes which comprises selecting a mixtureconsisting essentially of boron nitride and boride selected from thegroup consisting of zirconium boride, titanium boride, molybdenumboride, chromium boride, carbon boride and mixtures thereof, the borideamounting to 20% to 99% by weight of the mixture, placing the mixture ina mold and hot pressing said mixture at a minimum pressure of 500# persq. in.

10. A method of making bonded shapes which comprises selecting a mixtureconsisting essentially of boron nitride and boride selected from thegroup consisting of zirconium boride, titanium boride, molybdenumboride, chromium boride, carbon boride and mixtures thereof, saidmixture containing 1% to 50% by weight boron nitride, placing themixture in a mold and hot pressing said mixture at a minimum pressure of500# persq. in.

11. A method of making bonded shapes consisting essentially of boronnitride and a refractory boride selected from the group consisting ofzirconium boride, titanium boride, molybdenum boride, chromium boride,carbon boride and mixtures thereof, which comprises selecting a mixtureof boron nitride and boride, said mixture containing 1% to 50% by weightboron nitride, placing the mixture in a mold and hot pressing s'aidmixture at a minimum temperature of around 1600 C. and a minimumpressure of 500# per sq. in.

12. A raw batch for the manufacture of refractory bodies consistingessentially of boron nitride and a boride selected from the groupconsisting of zirconium boride, titanium boride, molybdenum boride,chromium boride, carbon boride and mixtures thereof the boride amountingto 20% to 99% by weight of the mixture.

13. A raw batch for the manufacture of refractory bodies consistingessentially of boron nitride and a boride selected from the groupconsisting of zirconium boride,

titanium boride, molybdenum boride, chromium boride, carbon boride andmixtures thereof, said boron nitride amounting to 1% to 50% by weight.

References Cited in the file of this patent UNITED STATES PATENTS1,991,204 Grenagle Feb. 12, 1935 FOREIGN PATENTS 478,6i6 Great Britain1938

1. AS A NEW ARTICLE OF MANUFACTURE, A BODY CONSISTING ESSENTIALLY OFBORON NITRIDE AND BORIDE SELECTED FROM THE GROUP CONSISTING OF ZIRCONIUMBORIDE, TITANIUM BORIDE, MOLYBDENUM BORIDE, CHROMIUM BORIDE, CARBONBORIDE, AND MIXTURE THEREOF, THE BORIDE AMOUNTING TO 20% TO 99% BYWEIGHT OF THE BODY.